1. Field of the Invention
The present invention relates to RF wireless modems for use in a laptop, Portable Digital Assistant (PDA), or similar device and more particularly, to RF wireless modems with integral, compact, horizontally-polarized, balanced, multi-element, directional antenna with integral balun.
2. Background
Recent advancements in electronics have improved the performance of RF wireless modems. For example, advancements in integrated circuit technology have led to high performance radio frequency (RF) circuits. The RF circuits are used to construct transmitters, receivers, and other signal processing components typically found in RF wireless modems. Also, advancements in integrated circuit technology have led to a reduction in the size of RF circuits, thereby leading to a reduction in the overall size of RF wireless modems. Similarly, advancements in battery technology have resulted in smaller, lighter, and longer lasting batteries used in RF wireless modems. These advancements have resulted in smaller and lighter RF wireless modems that operate for a longer period of time on a single charge.
A user of a RF wireless modem must be able to communicate with a wireless communication system's base station, which can be located in any direction from the user and radiates and receives RF signals that are generally vertically polarized. Historically, this has led to the use of vertically polarized antennas for RF wireless modems and other devices, such as cellular phones, that must communicate with wireless communication system base stations. Engineers have designed vertically polarized antennas ranging from simple quarter-wave vertical whips or monopoles, to vertical dipoles, to ¾ wave and ⅝ wave vertical antennas. Some examples of smaller vertical polarized antennas are the “pillbox” antenna, the inverted F antenna, the vertical polarized current loop antenna, and the vertically polarized patch antenna. Some engineers have also used balanced dipole antennas typically of ½ wavelength long.
Portable wireless communication devices such as pagers and cellular phones are used extensively today. For example, one such device is the conventional wireless messaging device, which now gives the user full text capability and makes return phone calls less necessary by providing access to information on anything from meetings for the day to local movie listings to the latest global news update. More elaborate, wireless messaging devices combine the benefits and flexibility of two-way messaging, the ability to run software applications, and personal computer connectivity with the wear-ability and convenience of a conventional wireless messaging device.
Electronic computing devices are also extensively used today. These computing devices can be fixed, such as a desk top computer, or portable. Portable computing devices in particular are becoming more and more popular. The portability of new electronic organizers PDAs, for example, combined with their longer battery life, larger memories, and safe storage of information, has caused a growth in popularity of these devices over the past few years. New functions such as the synchronization with a personal information manager has proven a major benefit for users of portable computing devices in both their personal and business lives.
Manufacturers of RF wireless modems, manufacturers of electronic computing devices, and wireless communication service providers are teaming up to produce integrated services and products including wireless applications capable of receiving text, numeric, or binary messages, and sometimes allowing clipped and full internet access, via RF wireless modems. These enterprise and consumer applications give electronic computing users the capability to receive wireless e-mail, up-to-the-minute news and stock reports, remote updates on interest rates and financial information, weather warnings, and many other applications yet to be imagined. For example, including a RF wireless modem in a computing device enables web-browsing over wireless network access provided by such current and future carrier technologies such as CDPD, CDMA, GSM, GPRS, UMTS, W-CDMA, Richocet, and other proprietary network technology using either circuit switched or packet switched technology.
The combination of portable and semi-portable computing devices and rf wireless modems presents new challenges to the RF engineer. For example, there are several problems that result from the integration of a RF wireless modem into an electronic computing device, such as limited antenna space for the RF wireless modem, the degradation of performance of the RF wireless modem due to electromagnetic interference (EMI) from the electronic computing device, the degradation of the performance of the electronic computing device due to transmitted RF energy from the RF wireless modems, and the degradation of the RF wireless modem receiving circuitry due to the transmitted RF energy from the RF wireless modem in full duplex systems.
EMI can affect an electronic system through conduction, radiation, or a combination of both. EMI control is a difficult design aspect for RF wireless modem integration into the electronic computing device, since there are so many combinations of EMI sources in the electronic computing device. Additionally, the very high sensitivity of the RF wireless modem's receiver and the close proximity of its antenna to the circuitry of the electronic computing device make it very susceptible to EMI. This high noise environment creates receiver desensitization when undesired EMI signals occur at the same frequency as the receive frequency, or at a number of other frequencies sensitive to the receiver circuitry (such as the intermediate frequency). Since the receiver cannot differentiate between the desired and undesired signals, the undesired EMI signal can block out the desired signals to desensitize or lower the sensitivity threshold of the receiver. If the amplitude level of the undesired signal can be lowered enough using EMI control techniques, the receiver's sensitivity threshold is not degraded or degraded an allowable amount.
One way to control EMI is to re-design the electronic computing device with EMI in mind. For example, making the housing of the electronic computing device a shielded box, using a dedicated circuit board layer as the ground-plane, using a ground-plane area underneath the RF wireless modem, or modifying the electronic circuit design to reduce the EMI emissions from the electronic computing device are all advantages approaches to controlling EMI. Since the electronic computing device is usually already in existence, however, and most manufacturers do not want to make changes to their electronic computing device, these type of major design modifications are not desirable. Therefore, the RF wireless modem must be designed to reduced susceptibility to the EMI emissions of the electronic computing device. Further, the RF wireless modem should not cause interference with the computing device, and it should fit within the space limitations of the electronic computing device.